The city’s construction business is mired in a spike of stalled projects, leaving vacant lots and half-finished buildings scattered around the five boroughs.

The number of stalled sites has risen by 17 percent since February, according to an analysis of city inspection records by the New York Building Congress.

“Projects are getting financed, getting under way and then getting stopped,” said Building Congress president Richard Anderson.

More than a quarter of currently stalled sites were added to the list in 2012.

The sudden spike in stalled projects has all but erased the progress made during a building boom of the previous 15 months, officials said.

“It’s perplexing to us,” said Anderson.

An average of 691 sites around the city were stalled during last month, compared with 592 in February.

November had the highest number of stalled sites since January 2011, according to the records.

It was also the seventh highest month since the city Buildings Department started keeping track of stalled construction sites in July 2009.

While some sites have been removed from the list as work has resumed, others have been added — and some sites around town seem to have been shut down indefinitely.

Forty-five percent of the sites currently stalled have been on the list since 2009, according to the Building Congress analysis.

“It’s become a long-term problem,” Anderson said.

He said it’s not clear why so many projects are stalled — but the spike “roughly coincided with a period of rather steep declines in the stock markets, as well as a growing uncertainty about the state of the world economy.”

Particularly hard hit are Brooklyn and Queens.

Brooklyn now has nearly half of all stalled sites in the city, 323 — up from 298 last year.

Queens ranks second, with 169 sites, after soaring from 129 a year ago.

In contrast, the number of stalled sites in The Bronx and Staten Island is unchanged from November 2011 and Manhattan’s total of 123 was reduced by four.

But the slowdown doesn’t appear to be hitting the luxury-housing market as hard as other sectors, Anderson said, noting that market value of the stalled projects is half a billion dollars lower than a year ago.

“This suggests that the luxury residential market was home to an outsized percentage of the projects that have resumed in 2012.”

City Councilman Steve Levin (D-Brooklyn) said he wasn’t shocked by the numbers because the market in his Greenpoint/Williamsburg district was so super-heated before the economy collapsed that construction was bound to fluctuate sharply.

“There were so many stalled sites that came out of the housing-bubble burst, I’m not surprised it’s slowing back down,” Levin said.

“It’s part of the ebb and flow of the housing market.”

The records also show that 45 percent of stalled sites remain vacant, meaning the developers are all set to go — they have the land and the construction permits — but haven’t started construction yet.